This invention relates to a method for vacuum drying of a substrate, such as a semiconductor wafer, and more particularly to a method for vacuum drying of a substrate applicable for a finer patterning of devices.
Conventionally, devices on semiconductor wafers have been fabricated by repeating a series of steps comprising film-forming, wafer processing step mainly consisting of lithography and etching, cleaning, and drying step. In particular, the technology for drying a substrate in the drying step is used to eliminate the residue of the ultrapure water used mainly in rinsing the cleaning liquid or the remaining moisture included in the cleaning liquid adhered to the substrate during the cleaning step. The conventional technology for drying a substrate can be roughly classified into spin-drying, organic solvent displacement drying, heat drying, and decompression drying.
However, due to the finer patterning and three-dimensional geometry of the devices in recent pursuit of a higher density of LSI, an event has arisen where none of the above drying technology can sufficiently dry substrates.
More particularly, in the processing step, contact holes or via holes to lead electrodes are formed after formation of interlayer insulator films accompanied with the finer and three-dimensional device structure, and the diameters and depths of such holes have become remarkably smaller and deeper due to the finer patterning of the devices. In the case where the pattern size of the LSI is approximately 0.5 xcexcm or less, it is quite difficult to physically blow out and eliminate the remaining moisture accumulated in and/or between high aspect ratio patterns which are mainly the contact holes or via holes by simply centrifugal force in the spin drying, and it is also difficult to dry the moisture after the moisture is simply displaced with organic solvent in the organic solvent displacement drying technology.
Therefore, particularly with the trend that the pattern size of the substrate has become smaller and smaller, several new drying technology have begun to be used. One of such technologies is known as IPA vapor drying method that displaces the water on the wafer with isopropyl alcohol (hereinafter referred to as IPA) by use of the vapor of heated IPA and also by use of the difference of vapor pressure between the IPA and pure water, and then places the whole substrate into the atmosphere or a reduced pressure atmosphere in order to immediately vaporize and eliminate the IPA with which the water is completely displaced. On the other hand, the Marangoni drying technology utilizing so-called Marangoni effect has been developed and used, which vaporizes the IPA with which the water is displaced, while the IPA being free-fallen on the wafer surface by use of the high permeability and high water-solubility of the IPA and also by use of the difference in surface tension gradients of the IPA and water.
However, due to the finer and three-dimensional device in recent pursuit of a much higher density LSI, the aspect ratio of the entire patterns which are mainly contact holes or via holes has been further increasing and then so-called low dielectric constant insulating materials have been developed and begun to be used.
More specifically, due to the finer patterning of devices, low dielectric constant insulating materials have been developed as interlayer insulating films in order to achieve high performance multi-layer interconnection wiring.
FIG. 3 and FIG. 4 are examples of magnified cross sectional views of the metal wiring layers formed on a finely patterned wafer immediately after the processing. As shown in FIG. 3 and FIG. 4, an insulating layer is formed on a silicon layer, and a contact hole or via hole H is formed running through the insulating layer. Low dielectric constant insulating material may be, for example, an inorganic or organic material (lowk A in FIG. 3) consisting of siloxane-family for Alxe2x80x94Cu, and a porous material (lowk B in FIG. 4) for Cu to achieve a lower dielectric constant.
The former siloxane-family material is weak against heat and thus its composition can be damaged when heated to above 200xc2x0 C., thereby the risk that moisture can be produced in the film, is increased. Moreover, depending on the conditions of the processing step, moisture can be produced in the film due to the effect of the processing step conditions themselves, or moisture can be impregnated in the film due to the ultra pure water used in the cleaning step after the processing step.
On the contrary, the latter porous material may be inorganic in most cases and can be an effective film to realize low dielectric constant, however, its porous structure presents a problem in that it tends to absorb moisture in the film inside.
In the interconnection wiring step, such moisture in the hole configuration or in the film which forms the device can be the main cause for corroding metal wiring due to the reaction due to the remaining moisture in the hole after the wirings being formed and the metal of the wiring material, or may be the cause of after-corrosion due to the occurrence of cracks in the insulating films.
Either of them may be significant loss of quality to the semiconductor wafer products.
Accordingly, it is essential to completely eliminate the moisture remaining in the device prior to the film-forming processing.
In this respect, it is necessary to raise the temperature of the wafer for the conventional heat drying technology, which may require excessive heating (for example, over 100xe2x96xa1) in order to effectively eliminate the moisture impregnated in the insulating film. In this case, the risk can be increased such that the heat causes deterioration or damage to the device itself that is formed on the wafer surface. Moreover, in the recent ultra-finer patterning devices, the applied heat tends to cause pattern deformation or film deterioration because of the unevenness of the high aspect ratio patterns which are mainly contact holes or via holes formed on the wafer surface. Particularly, in the case that the interlayer insulating film is a siloxane-family material, the heat in the presence of oxygen adversely results in additional moisture produced in the film as described above.
Therefore, it is quite difficult or almost impossible to effectively dry and eliminate the moisture impregnated inside only by the heat drying, maintaining device quality.
On the other hand, in the conventional decompression drying technology, it is necessary to increase vacuum pressure and physically evacuate the inside moisture out of the wafer surface in order to effectively eliminate the moisture impregnated in the insulating film, increasing high vacuum pressure. However, due to the unevenness of the high aspect ratio patterns which are mainly contact holes or via holes formed on the wafer surface, even if the high vacuum pressure is increased, the inside moisture cannot be evacuated or, even if possible, it takes a significant amount of time due to the effect of the surface tension of the water remaining in the holes or the effect of the hydrophilic deposition film. Particularly, in the case that the interlayer insulating film is a porous material, it is difficult to physically evacuate the moisture in the holes because of its porous structure.
In the conventional drying technology using IPA, it is quite difficult to diffuse the IPA into water within a specified time period (for example within 2 minutes), and it is difficult to eliminate the water. Moreover, the IPA is designated as a hazardous material under the Fire Defense Law and is classified to alcohol in the 4th category, therefore and it is flammable and explosive, it is desirable to avoid the use of the IPA from the point of view of safety and control cost, if possible.
In view of the above, a drying technology which can cope with various aspects such as electric reliability, cost, and safety in finely patterning the devices is strongly needed recently.
Embodiments of the present invention can also provide a vacuum drying method for substrates which can eliminate in a short time not only the moisture adhered to the wafer surface but also the moisture impregnated inside the film that forms the device without deforming or deteriorating the device formed on the wafer in the drying step.
In addition, embodiments of the present invention can provide a vacuum drying method for substrates which can dry and eliminate the moisture adhered to the wafer by adjusting the heating temperature and/or vacuum pressure depending on the fine patternings formed in the devices.
To solve the above-mentioned problems, the preferred embodiment of the present invention provides a vacuum drying method for substrates. The preferred method includes drying a substrate by processing the wafer surface in a desired condition, cleaning the processed substrates with cleaning liquid, and drying the cleaned substrates. For example, the drying step can include: detaching the moisture from the substrate to outside heating the substrates surface to a predetermined temperature, and vaporizing the moisture of the surface above-mentioned as vapor: and eliminate the moisture from the substrate vacuuming the detached vapor at predetermined vacuum pressure.
In addition, the moisture of the surface can be the moisture impregnated in and/or between the fine patterns formed on the substrates or the moisture impregnated inside the insulating film consisting of the fine patterns.
Further in addition, the moisture may be the moisture included in the processing liquid and/or the cleaning liquid, and/or the residual of ultrapure water used in rinsing the processing liquid and/or the cleaning liquid.
In addition, the method further comprises a step of previously placing the substrates to be dried in a vacuum atmosphere at a vacuum pressure so that the evaporating temperature of the moisture can be lowered.
Moreover, the heating step to a predetermined heating temperature is preferably performed by radiation heating from outside of the vacuum atmosphere.
In addition, preferably, the vacuuming step to vacuum pressure is performed by a cryopump, and the cryopump adsorbs and collects the vapor detached from the wafer.
Although the vacuum drying method for substrates of the present invention is a drying technology combining the conventional heat drying technology with the depression drying technology, the methods are not a mere combination of both drying technology but is characterized by having synergistic effects of both technology.
According to the vacuum drying method for substrates of the present invention, it is possible to vaporize as vapor not only the residual moisture on the substrates surface after the cleaning but also the moisture in the inside films consisting of fine patterns, by heating the substrates surface to a predetermined temperature.
More specifically, it is possible to vaporize the moisture as vapor not only on the substrates surface but also accumulated in and/or between the high aspect ratio patterns which are mainly contact(s) holes or via holes or the moisture impregnated inside the insulating film consisting of the patterns from inside of the insulating film to outside. By placing the substrates to be dried in a vacuum environment at a vacuum pressure prior to the heat drying, effective heating can be achieved particularly by radiation heating while the evaporating temperature is lowered under a high vacuum pressure. In addition, by the radiation heating particularly by using near infrared rays, inside heating can be achieved with avoiding the damage(s) on the substrates surface by heat.
Then, by vacuuming the vapor detached from the substrates, the moisture can be eliminated from the substrates.
As described above, the heat drying enhances the detachment of the moisture from the substrates by the phase change from the liquid into the vapor, while the vacuum drying eliminates the vapor detached from the substrates completely, vacuuming the moisture from the substrates.
In this case, when only the heat drying is performed, some insulating films may be damaged or deteriorated by the heat or moisture occurrence may be adversely caused inside the insulating films by the heating in the presence of oxygen.
On the other hand, when only the vacuum drying is performed, even if the vacuum pressure in the atmosphere may be higher, it is almost impossible to or if it is possible it takes considerable amount of time to evacuate and eliminate the moisture accumulated in and/or between the high aspect ratio patterns which are mainly contact holes or via holes in and/or the moisture impregnated in the insulating film(s) directly from in and/or between the high aspect ratio patterns, or in the insulating film(s) in its liquid phase.
From this angle, by the concomitant use of both methods, that is, by heating the moisture accumulated in and/or between the high aspect ratio patterns or the moisture impregnated in the insulating films to vaporize while the evaporating temperature is lowered under decompression pressure and to detach the moisture from in and/or between the high aspect ratio patterns which are mainly contact holes or via holes or in the insulating films into the atmosphere, and then by immediately vacuuming the detached moisture, the vaporized moisture can be completely eliminated.
In this case, a drying method can be provided which can cope with the finer patterning by adjusting the heating temperature in the heat drying and the vacuum pressure in the vacuum drying according to the processing technique of the interlayer insulating films and/or cleaning technique.
In one aspect, the present invention provides a vacuum drying method for substrates which can effectively dry the wafer on which finely patterned devices are formed.